Interactions between reserve mobilization and regulation of nitrate uptake during regrowth of Lolium perenne L.: putative roles of amino acids and carbohydrates

Abstract

Louahlia, S., Laine, P., Macduff, J. H., Ourry, A., Humphreys, M. O., Boucaud, J. (2008). Interactions between reserve mobilization and regulation of nitrate uptake during regrowth of Lolium perenne L.: putative roles of amino acids and carbohydrates. ?Canadian Journal of Botany, 86, (10), 1101-1110. (now Botany) IMPF: 01.08 RONO: 1310 3001In most forage grass and legume species the recovery of leaf growth following severe defoliation depends on mobilization of carbon and nitrogen reserves from the remaining tissues. Unusually, Lolium perenne L. is able to compensate for low levels of available N storage compounds by rapid up-regulation of mineral N uptake. To investigate the physiological basis of this behaviour, perennial ryegrass plants were exposed to a 10 ?d period of optimal mineral N (high-N plants) or zero N (low-N plants) supply before defoliation. N deprivation decreased total N and amino acid concentrations in roots, and increased root water soluble carbohydrate concentrations. Compared with high-N plants (control), fructans and fructose concentrations in roots of low-N plants were 74% and 49% higher, respectively. Low-N plants had higher rates of nitrate uptake following defoliation, and lower amino acid concentrations in the roots (mainly as asparagine and glutamine); a causal role was suggested by the inhibition of nitrate uptake by external root supply of amino acids to low-N plants or by a stimulation of N uptake of high-N plants by sucrose supply to the roots. The results suggest that down-regulation of nitrate uptake following defoliation of plants with high levels of N reserves, may be effected through an increased cycling of amino acids within the plant and by a shortage of carbohydrates. Results are discussed in relation to the proteolytic activities and mobilization of C and N reserves to leaf meristem.Peer reviewe

Enzymatic Metabolism of Nitrogen in Leaves and Roots of Creeping Bentgrass under Nitrogen Deficiency Conditions

“…We observed that AA content in young and old leaves and in roots decreased as a result of N deficiency (Fig. 2), which is consistent with a report that N deprivation decreased AA content in perennial ryegrass roots (Louahlia et al, 2008). Free AAs were the predominant storage compounds of reserve N for the regrowth of the bushgrass (Calamagrostis epigejos) after defoliation (Kavanová and Gloser, 2005).…”

“…In the roots, the NAD + -dependent GDH deamination activity decreased as a result of 28-d N deficiency in comparison with the +N treatment. Previous studies have shown that N deficiency stimulated export of assimilates to roots of darnel (Lolium temulentum) (Powell and Ryle, 1978) and increased root watersoluble carbohydrate of perennial ryegrass (Louahlia et al, 2008). The lower deamination activity observed in roots of N-deficient plants in the present study may suggest that a higher level of carbohydrate in the roots of -N plants may suppress the deamination activity, whereas a lower level of carbohydrate in the roots of +N plants may stimulate the deamination activity.…”

Growth and Physiological Response to Nitrogen Deficiency and Re-supply in Leaf-vegetable Sweetpotato (Ipomoea batatas Lam)

“…In this study, N deficiency significantly decreased essential amino acids, including Lys, Phe, isoleucine (Ile), tryptophane (Trp), leucine (Leu), and valine (Val) content, and nonessential amino acids, consisting of glutamic acid (Glu), aspartic acid (Asp), Gly, argnine (Arg), and proline (Pro) content in both cultivars (Table 4). The general downregulation of amino acids in N-starved plants is expected and in agreement with many other studies in perennial ryegrass (Louahlia et al, 2008), Arabidopsis (Krapp et al, 2011), wheat (Howarth et al, 2008), tomato (Urbanczyk-Wochniak and Fernie, 2005), and tobacco (Fritz et al, 2006). Under control growth conditions (sufficient N, S-N), 'Pushu 53' had higher lysine (Lys), phenylalanince (Phe), glycine (Gly), and histidine (His) content than 'Tainong 71' (Table 4).…”

Can we understand and predict the regulation of biological N2 fixation in grassland ecosystems?

“…Several studies have shown that amino acids (especially glutamine and asparagine) supplied to roots by the phloem are implied in the specific regulation of NO 3 -uptake and in its coordination with photosynthesis (Muller and Touraine 1992;Delhon et al 1996;Malagoli et al 2004;Louahlia et al 2008). A feedback regulation of NO 3 -uptake by the N demand of the plant was also observed in N 2 fixing clover lines .…”